1. Field of the Invention
The present invention relates to the construction of an active matrix display device such as an active matrix liquid crystal display (LCD) device.
2. Description of the Related Art
In an active matrix LCD device, thin-film transistors are arranged on a sheet of quartz or glass at a high density. It is increasingly required in recent years to raise the level of integration of the thin-film transistors. On the other hand, it is more and more required for the LCD device to provide larger display areas to meet the growing demand for large-screen displays. This is where the LCD device greatly differs from large-scale integrated (LSI) circuits which are required to provide higher integration levels and smaller physical sizes.
Besides the requirement for large-screen display, it is desired to make conductor lines of the LCD device as narrow as possible so as to provide an increased aperture ratio. If, however, narrow conductor lines are used, problems arising from their increased resistances will become evident.
The active matrix LCD device requires means for masking the thin-film transistors arranged in individual pixels as well as masking means, which is known as a black matrix, for masking edges of individual pixel electrodes. Generally, these masking means including the black matrix are separately arranged from the conductor lines. Such a construction is not preferable though because it complicates processing steps needed for the production of the active matrix LCD device.
One method for reducing conductor line resistance is to use aluminum as a wiring material. However, the use of aluminum could give rise to reliability problems because electrical contacts between aluminum and semiconductor and between aluminum and a transparent conductive coating, which is usually a thin layer of conductive oxide such as indium tin oxide (ITO), are liable to become unstable.
It is an object of the present invention to provide a construction of an active matrix LCD device, by which an increased aperture ratio is obtainable with a small number of steps in the overall manufacturing process. It is a further object of the invention to provide a construction which can eliminate instability of electrical contact caused by specific wiring materials.
According to the invention, a semiconductor device comprises a conductor line for interconnecting a semiconductor element and a conductive oxide film, the conductor line having a layer structure including an aluminum film sandwiched between a pair of titanium films, wherein one of the titanium films is held in contact with the semiconductor element while the other titanium film is held in contact with the conductive oxide film.
In one specific form of implementation of this construction, a drain region of a thin-film transistor is connected to a pixel electrode constructed with ITO by the conductor line which is formed by sandwiching the aluminum film with the pair of titanium films. More particularly, the drain region made of a semiconductor material is held in contact with one titanium film while the pixel electrode constructed with ITO is held in contact with the other titanium film. This construction provides a solution to the reliability problem arising from the instability of electrical contact between aluminum and semiconductor.
This construction also serves to improve the quality of contact between ITO and the conductor line as the latter is covered by the titanium film. In general terms this means that the invention provides a solution to the reliability problem arising from the instability of electrical contact between aluminum and ITO (or a conductive oxide film in general) as well. Needless to say, an additional advantage comes from the use of aluminum of which resistance is remarkably low.
In a varied form of the invention, a semiconductor device comprises a conductive oxide film which constitutes a pixel electrode, a conductor line for interconnecting the conductive oxide film and a drain region of a thin-film transistor, a first masking film constructed with the same material as the conductor line for masking the thin-film transistor, and a second masking film constructed with the same material as the conductor line for masking edges of the pixel electrode, wherein the conductor line has a layer structure including an aluminum film sandwiched between a pair of titanium films.
As will be discussed later in greater detail, the semiconductor device thus constructed has the pixel electrode constructed with ITO. the conductor line connecting the pixel electrode to the drain region of the thin-film transistor and the first masking film for masking the thin-film transistor. The conductor line has a three-layer structure in which the aluminum film is sandwiched between the pair of titanium films. In addition, the second masking film, or the black matrix, constructed with the same material as used for producing the conductor line masks the edges of the pixel electrode.
What is significant in this construction is that the conductor line, first masking film and black matrix are obtained simultaneously by patterning the same three-layer structure. This serves to simplify the overall manufacturing process, improve production yield and reduce manufacturing costs.
The titanium films are most preferable for sandwiching aluminum from the viewpoint of electrical characteristics in this invention. Chromium films may be employed instead of the titanium films, if desired. However, titanium is more desirable since the titanium film can be more easily patterned by dry etching than the chromium film. Furthermore, a few percent by weight of appropriate impurities may be added to the titanium, to adjust their optical and/or electrical characteristics.
In yet varied form of the invention, a semiconductor device comprises a conductive oxide film which constitutes a pixel electrode, a first conductor line for interconnecting the conductive oxide film and a drain region of a thin-film transistor, a masking film constructed with the same material as the first conductor line for masking the thin-film transistor, and a masking film constructed with the same material as the first conductor line for masking edges of the pixel electrode, a second conductor line connected to a source region of the thin-film transistor, an outgoing conductor line constructed with the same material as the first conductor line, the outgoing conductor line being connected to the second conductor line, wherein the first conductor line has a layer structure including an aluminum film sandwiched between a pair of titanium films.
In one specific form of implementation of this construction, the first conductor line has a three-layer structure in which the aluminum film is sandwiched between the pair of titanium films while the second conductor line is constructed with a titanium film and an aluminum film. The first conductor line, first masking film, black matrix and outgoing conductor line can be formed by patterning the same three-layer structure.
Accordingly, the invention provides a highly reliable construction of semiconductor devices, eliminating instability of contact between wiring materials. The three-layer conductor line configuration is particularly effective in view of low resistance of the aluminum film and good electrical contact between the titanium film and semiconductor and between the titanium film and conductive oxide film.
Remarkable features of the invention can be summarized as follows:
(1) The stacked two-layer structure including the aluminum and titanium films helps reduce voltage drop in individual source lines, and this is particularly evident in large-screen LCD devices;
(2) The stacked two-layer structure including the aluminum and titanium films enhances the reliability of connections between the individual source lines and source regions;
(3) The three-layer structure of individual first conductor lines interconnecting drain regions and pixel electrodes can be used for producing the masking film for masking each thin-film transistor without requiring any additional processing step;
(4) Individual outgoing conductor lines used for connecting to surrounding circuit elements can be created at the same time with the first conductor lines, and the reliability of connections between the individual first conductor lines and source lines can be improved;
(5) The reliability of connections between the first conductor lines and drain regions and between the first conductor lines and ITO pixel electrodes can be improved; and
(6) The black matrix can be formed at the same time with the first conductor lines.
As will be recognized from the foregoing discussion, the invention makes it possible to simultaneously produce various elements of the active matrix LCD device without requiring additional processing steps. Moreover, the invention provides improvements in product performance and reliability as well as a reduction in manufacturing costs.